1. Field of the Invention
The present invention relates to embedding data in material. “Material” means one or more of still images, video material, audio material, and data material. Material is represented by information signals which most preferably are digital signals.
2. Description of the Prior Art
It is known to embed data in material to identify the ownership of the material and/or to trace the provenance of the material to detect and protect against copyright infringement. Such embedding of data is known as watermarking.
Watermarks may be “robust” in that they are difficult to remove from the material. Robust watermarks are useful to trace the provenance of material which is processed in some way either in an attempt to remove the mark or to effect legitimate processing such as video editing or compression for storage and/or transmission.
In the case of images, whether still or moving, a visible watermark is useful to allow e.g. a customer to view the image, e.g. over the Internet, to determine whether they wish to buy it but without allowing the customer access to the unmarked image they would buy. The watermark degrades the image and the mark should not be removable by the customer. Visible watermarks are also used to determine the provenance of the material into which they are embedded. Watermarks may also be applied to audio material and to other data.
It is known to use “Digital Rights Management” software to protect material against misuse. Many companies provide such software, e.g. SealedMedia, Microsoft, InterTrust Technologies, and others. Such software, which is designed to be secure against unauthorised modification, allows the providers of material to securely distribute material over computer networks and to control the use of the material by users.
U.S. Pat. No. 4,890,319 discloses a subscription television system for distributing programme material protected by copyright to subscribers. The system comprises a transmitter including a data insertion circuit for inserting a control bit in a transmitted signal comprising other control data and the protected programme material. A receiver of the system includes a memory for storing a pre-assigned subscriber identification. Upon receipt and identification of the control bit at the receiver, the receiver inserts the subscriber identification into the programme material so that any unauthorized copy made of the programme material may by found to include the subscriber identification. The addition of the user identification is imperceptible to the user but will show up on any copies of the programme material. The user identification is inserted into a television programme “for but a single frame” and “is barely detectable to the subscriber's eye, such that no significant impairment in picture quality results”.